I have had this over the past few months. Took it to Diamond Motors and did some investigation and data logging with Mick there. The key thing to do is get the fault codes read on a CLIP computer. Mine turned out to have an injection ECU internal fault logged (DF038 1.DEF). This fault is not very helpful, though, as it can be caused by a true fault in the injection ECU (dry joint), or a bad voltage supply (old battery), bad earth (corroded earth strap), or as it turned out with me, bad signals from some component going outside of acceptable parameters. Anyway, read on if that's the fault you have...
We tracked mine down to being likely to be an issue with the throttle pedal potentiometers. The pedal unit has two pots in it, and the ECU averages the measurement to get an indication of position. We logged the voltages on each pot and one was very, very noisy. The injection ECU clearly therefore has a maximum variance between the two pot readings, over which it thinks there is a fault (e.g. problem with one of the analog to digital converters in it), and throws the only fault code it can - the internal fault code. I bought a pedal from a 197 that was being broken and haven't had any issues since.
My advice would be to initially get some electrical contact cleaner and undo every plug you can see in the engine bay, like MAF sensor, coil packs, throttle body, and if you're feeling brave (I didn't, I got Mick at Diamond to do it) the injection ECU connectors too - you'll need to unplug the battery for that. We also did the plug for the throttle pedal. Just in case it is an issue with the throttle body, you can remove it and give it a good clean out - mine had a bad build up of oily gunk.
Then get the fault codes read by a reputable garage, and don't just believe them if they say you need a new ECU as it could be something a lot simpler! The Clio workshop manual has a list of all of the fault codes and the recommended fixes and further diagnostics to be carried out.
Joe
